Goggles, respirators, masks, helmets, eyewear, protective devices, and the like generally include lenses, visors, windows or other transparent or translucent optical materials for the user to look through. It is important to be able to see through such optical materials, in whatever form or shape they may take. Unfortunately, the visibility through such optical materials is sometimes compromised by environmental conditions. For example, optical materials in goggles, masks, or other protective devices sometimes get fogged by the user's respiration, by differences in temperature or humidity, or by other environmental factors such as the adsorption or deposition of smoke or other airborne particles.
It is useful to assess the performance of the optical materials of a particular device or configuration by evaluating the reduction in visibility through the optical materials due to fogging or other environmental factors. Such assessments can be difficult, however, especially when performance is assessed under a variety of conditions, or by different investigators or parties within a commercial production chain. Although lens fogging tests have been performed in the past, the results have generally been expressed in terms that are divorced from a meaningful assessment of visibility. For example, prior art methods of measuring performance of optical materials have largely been subjective, and have often failed to provide meaningful results that are applicable to a wide range of optical materials or environmental conditions.